I just noticed my Stinson motor as soon as I cut throttle it stops right away. Also noticed it's hard to turn by hand. Other than that it runs fine. Doesn't get hot or have an odor when throttle is applied and seems to preform fine. Will it eventually seize? Anything I can do?

It might be the ESC brake. It shorts out the windings to stop the motor.
Disconnect it from the ESC if you want to be sure.
Most ESCs can also be programmed to turn the brake on or off. Which ESC is it?

It's normally used for folding props to ensure they stop windmilling and fold properly. When the brake is set, it's a bit like having a short across the motor, it's noticeable even with no battery connected.

Even without folding props, braking the prop is often recommended if you want to stop the motor completely. A free-wheeling prop induces more drag than a braked prop, at least for props 9 or 10" in diameter or larger. That fact can improve your landings even. If you keep your motor turning (keep a touch of throttle on) you can bring some planes in a bit steeper and cleaner.